User login

Search

Úvod

Submitted by Pavel Hejda on Thu, 03/06/2008 - 17:01.

Space Weather

On planet Earth violent weather phenomena such as snowstorms and thunderstorms occur. Other types of storms can occur in space. They are known as "solar storms" and like their counterparts on Earth they too may cause problems for us humans, especially because we are so dependent on satellite technology. The effects that these "solar storms" can cause are usually only relevant for space-borne systems, but in extreme cases effects may be registered all the way down on Earth. Before we present these "solar storms" and their potential consequences on us humans let us first understand what our location in space has to do with everything.

The Heliosphere

The “space” between the planets in our solar system is what we call interplanetary space, better known as the heliosphere. “Helios” is the ancient Greek word for the “Sun” and the prefix is used to describe the space environment between the planets which is under the influence of the Sun.

Helios was the Sun god in Greek mythology and was thought to ride a chariot drawn by horses through the sky, bringing light to Earth.

To better visualize the heliosphere one can imagine a vast magnetic bubble (see below figure) containing the solar system (Sun and planets), the solar wind and the interplanetary magnetic field, as well as numerous “cosmic ray” populations, and dust.

Schematic representation of the heliosphere. Courtesy of NASA.

Indeed, interplanetary space is not void at all and the space environment has a weather of its own - its own space weather. Our local space weather is a function of Earth's location in the solar system, the behaviour of the Sun and the nature of Earth's magnetic field and atmosphere. Space weather can be defined as how solar activity may have unwanted effects on both technological (both space-borne and situated on Earth) and biological systems (in space and at airline altitudes). Even though you may not be aware of it, space weather affects everybody, either directly or indirectly. Before we go into more detail, let us first introduce the Sun - the driver of our local space weather.

Our Local Space Weather Driver

Though just an average star our Sun is very dynamic and has many interesting features. The Sun has an approximate 11-year cycle described by its activity. When activity is low the solar cycle is at minimum and when the situation is the opposite we have what is called solar maximum. Signatures of the solar cycle can be observed by telescopes and detectors on satellites, and consequently one can observe the Sun with different "glasses". What this physically means is that one performs observations at different wavelengths. This allows one to observe different heights of the Sun. For example, with X-ray observations we can study the solar corona and see when solar activity phenomena manifest themselves. On the below figure we see the changing Sun as observed in X-ray from solar maximum (left side) to solar minimum (right side). When at minimum no manifestations are observed.

The changing Sun as observed in X-ray. Courtesy of SXT/Yohkoh.

Why is Space Weather Interesting for Us ?

Why is space weather of interest for Earth? There are many answers to this question. First of all present society on Earth is deeply dependent on reliable space systems and will be more so in the future and these systems are vulnerable to space weather. In parallel technical systems are becoming more sensitive to the space environment and will continue so in the future due to developments in technology such as miniaturization. Finally there are developments in the future where space weather will be very important (e.g., Mars colonies, asteroid mining, space tourism, space hotels, transportation technology, commercial opportunities on the International Space Station (ISS), solar power, etc.).

Luckily for us "solar terrestrial physics" science, the study of how the Sun and Earth are connected, has progressed to a stage where useful space weather models and predictions are in development and in some cases already exist. It is important that we are able to forecast the weather in space like we do the weather on Earth, but forecasting must be complemented with mitigation techniques. On Earth we have homes to protect us from the environment. In space satellites are protected by shielding techniques. Like a raincoat the shielding protects the astronaut in the spacecraft from the space environment. However sometimes the raincoat is not sufficient and further procedures need to be taken (for example the astronaut needs to enter a special shelter on the spacecraft). That is where forecasting becomes extremely important - warning us when such space weather events occur.

Space Weather Phenomena occurring in the near-Earth Space Environment

Energetic charged particles

For Earth orbiting satellites and interplanetary missions the three most important components in the heliosphere are:

1. Earth's Radiation Belts (trapped protons and electrons), also known as the Van Allen Belts.